1. Field of the Invention
The present invention relates to chucking apparatus, and more particularly, to such apparatus for applying screw-type caps to containers at a constant torque.
2. Description Relative to the Prior Art
Various types of chucking apparatus are known in the art for applying caps to containers. In general, the construction of such apparatus varies depending upon the particular characteristics of the cap and container. For example, U.S. Pat. No. 1,050,788 discloses bottle capping apparatus suitable for use in applying press-type caps to milk bottles. The capping apparatus comprises an upright guide member resembling a pipe section in which disc shaped caps are vertically stacked. A series of latches operate to drop the lowermost cap in the stack on the bottle mouth. A pusher element is provided which seats the cap by pressing it into the mouth of the bottle. One advantage of capping apparatus of this type is that the caps are stacked inside a pipe-like guide member from which they are dropped one at a time onto the mouth portion of uncapped bottles. This type of cap feeding arrangement is commonly known as center feeding. Apparatus of the center feed type do not require the additional and often complex cap handling apparatus of other cap feeding arrangements, discussed below. All that is needed is a chute or conveyor to drop the caps into the pipe-like guide member. For those applications wherein screw type caps are to be applied to a container, however, it would appear that the bottle capper disclosed in U.S. Pat. No. 1,050,788 is of little use.
U.S. Pat. Nos. 2,705,101 and 2,884,751 disclose container capping apparatus suitable for use in applying screw-type caps. Both of these patents are similar in that the capping apparatus disclosed therein comprises a closure gripping element, i.e., a chuck device, which rotates in order to screw a cap held thereby onto a threaded portion of a container. The chuck devices themselves, however, are of different construction. Because the present invention concerns, inter alia, a chuck device of a particular construction, it is of interest to consider the chuck devices of the above patents in more detail.
The chuck device of U.S. Pat. No. 2,705,101 comprises an annular collar of a resilient, compressible material such as rubber. The opening of the annular collar is only slightly larger than the cap. Mechanical pressure is applied to the compressible collar which causes the opening to close enough to grip a cap positioned within the collar. The chuck device then rotates to screw the cap onto the container. A friction clutch is connected to the chuck device to regulate the degree of the tightness with which the cap is screwed on the container.
The chuck device of U.S. Pat. No. 2,884,751 is similar to the chuck device described above in that an annular resilient member is deformed to grip a container cap. Unlike the above-described chuck device, however, the annular resilient member is in the form of a diaphragm which covers an annular channel in the chuck device. Air under pressure is introduced into the channel causing the resilient diaphragm to bulge, thereby coming into gripping engagement with the cap. The cap is then applied to the container in a manner similar to that described in connection with the chuck device of U.S. Pat. No. 2,705,101.
Because resilient members are used for gripping, both of the chuck devices described above are well suited for applications wherein it is important not to mar, scratch or otherwise damage the container cap. But because resilient members are used for gripping, the torque with which a cap can be applied is limited by the frictional engagement between the cap surface and the gripping portion of the resilient member. If a cap has a smooth surface and is contaminated with foreign matter, the frictional engagement is very low and the cap will easily slip within the chuck device. Further, imperfections in the cap threads on the threaded portion of the container may produce enough resistance to start the cap slipping, thereby preventing the cap from being fully tightened on the container.
Apart from the chuck devices themselves, a significant disadvantage of the type of capping apparatus disclosed in U.S. Pat. Nos. 2,705,101 and 2,884,751 is that additional cap handling apparatus is required to present the caps to the chuck device. In U.S. Pat. No. 2,884,751, for example, a rotary disc is provided upon which caps, which have been properly positioned and oriented, are supported. The disc rotates to sequentially feed the caps to a station for pick up by the chuck device. Such a cap feeding arrangement will be referred to as bottom feeding, as opposed to the center feeding arrangement discussed above in connection with U.S. Pat. No. 1,050,788. Center feeding is generally not compatible with screw type capping apparatus because the chuck device, which rotates, is normally mounted on a shaft which prevents caps from being fed to the chuck device from above. Further, even if the caps were somehow fed to the chuck device from above, a delicate timing scheme would apparently be necessary to grip the cap at precisely the proper time to prevent it from falling through the chuck.
Another disadvantage of the prior art chuck devices is that each is capable of handling a cap of only one size, and is not readily adaptable for universal application.